Neuron and Neural Firing Process Notes

The Neuron

  • Unit 2: Biological Bases

Learning Targets

  • 2.F Identify basic processes and systems in the biological bases of behavior, including parts of the neuron.
  • 2.G Identify basic process of transmission of a signal between neurons.

Parts of the Neuron

  • Dendrites: Receive incoming messages.
  • Cell Body (Soma): Contains the nucleus.
  • Nucleus: Makes the decision to fire or not fire.
  • Myelin Sheath: Fatty tissue that insulates the axon, speeding up transmission of the message.
  • Node of Ranvier: Space between myelin sheath.
  • Axon: Longest part of the neuron which the electrical message travels the length of.
  • Schwann Cells: Non-neuronal cells in the CNS that form myelin sheath.
  • Axon Terminal Buds: The end point of a neuron that releases neurotransmitters into the synapse, hence sending the message on to the next neuron.

Neural Firing Process

  • Resting Potential: When a neuron is NOT firing, and has a negative charge with mostly potassium ions inside and mostly sodium ions outside.

Polarization

  • Neuron is ”polarized,” when opposites are AWAY from each other. Polarization – at resting potential, when sodium is on the outside, potassium on the inside of a neuron.
  • At this state, the neuron is at homeostasis – it’s normal, happy, resting state. The state at which is strives to obtain regularly.

Action Potential

  • “Nerve impulse” – the electrical pulse or “message” that travels the length of the axon.

All-or-Nothing Principle

  • When the nucleus decides to fire, it fires down the axon completely (all the way) or not at all.
  • Likewise, maintaining the same intensity (strength/power of message) the entire length of the axon.

Toilet Analogy

  • Think, discuss, and write about how it is similar to a toilet and its “firing” process.

Depolarization

  • When ”opposites” are no longer away from each other. This happens with action potential like a domino effect… sodium (and +) ions rush in, causing potassium (and -) ions to rush out

Refractory Period

  • The period of time after firing that the neuron is focused on resetting, and therefore is unable to fire again.
  • Sodium goes back out… So then potassium feels good about going back in.
  • Reflect with a partner again… how is refractory period similar to a process of a toilet flushing?

Ion Channels

  • Sodium channels open and sodium ions rush in.
  • Potassium channels open and potassium ions rush out.
  • The first sodium channels close, but channels further down open causing the process to go the length of the axon.

The Synapse

  • Sending Neuron
  • Receiving Neuron
  • Action Potential
  • Neurotransmitters: Chemical substance that crosses the synapse to carry on the message to the next neuron
  • Synapse: Open space between two neurons at which neurotransmitters cross.
  • Receptor sites: Specific points on dendrites of neurons that receive specific types of neurotransmitters.
  • The synapse is simply a gap, open space between neurons, and therefore NOT a part of the firing process.

Neurotransmitters

  • Acetylcholine:
    • Primary Roles: Muscle contractions, memory, and learning
    • Associated Disorders: Alzheimer’s disease
  • Dopamine:
    • Primary Roles: Movement, thought process, Rewarding sensation
    • Associated Disorders: Parkinson’s, Schizophrenia, Drug addition
  • Serotonin:
    • Primary Roles: Emotional states, sleep
    • Associated Disorders: Depression
  • Norepinephrine:
    • Primary Roles: Physical arousal, learning, and memory
    • Associated Disorders: Depression, stress
  • GABA:
    • Primary Roles: Inhibition of brain activity
    • Associated Disorders: Anxiety disorders
  • Endorphins:
    • Primary Roles: Pain perception, positive emotions, “runners high”
    • Associated Disorders: Opiate addiction

Agonists vs. Antagonists

  • Both are OUTSIDE (external) substances that somehow interact with neurotransmitters at the receptor sites on dendrites of a neuron
  • Both interact differently at the receptor sites.

Key Analogy:

  • House Key
  • Master Key
  • Fake or wrong key

Agonists

  • MIMIC neurotransmitter activity
  • Fitting in the receptor site like a master key – it works just like the original key but is not exactly the same

Antagonists

  • BLOCK neurotransmitter activity
  • Fitting in the receptor site like a fake key, preventing the neurotransmitter from getting to its receptor site and doing its job.

Agonists Examples

  • Morphine (opiate derivative) mimics endorphins
  • Think of the effects of morphine (anesthesia)… how does that make sense given the role of endorphins?

Antagonists Examples

  • Botox (form of botulism) blocks Acetylcholine
  • Think of the role of acetylcholine… how does it make sense that botox would block it’s ability to do its job?